Would such person become president or acting president?
He would have to get any judge or any other officer with notarial powers to swear him in.
I see no mention of such a thing with taking the oath.
It'd probably help if he had a witness.
Before he enter on the Execution of his Office, he shall take the following Oath or Affirmation:
"I do solemnly swear (or affirm) that I will faithfully execute the Office of President of the United States, and will to the best of my Ability, preserve, protect and defend the Constitution of the United States."